Thus a message transmitted by a first node, called the source, to a second node, called the destination, remote from the first node, can pass through a third node constituted by a terminal of the network. A routing protocol adapted to the network is used for determining this possible third node, as well as the other possible nodes through which the message passes.
From among multihop networks, it is possible to mention the mesh networks, for example WiFi mesh networks, and the Ad Hoc networks. The latter can implement wireless communications and comprise relatively mobile nodes.
Certain routing protocols, called proactive, provide for each node of the network to keep updated a routing table and to broadcast control data in order to estimate the topology of the network. It is for example possible to refer to OLSR (Optimized Link State Routing) and TBRPF (Topology Broadcast Based on Reverse-Path Forwarding).
Other routing protocols, called reactive, provide for a generation of paths between the source node and the destination node only when requested by the source node. It is possible to refer to AODV (Ad hoc On-Demand Distance Vector Routing) and DSR (Dynamic Source Routing).
It is well known that the transmission of digital data, whether by wire or wireless, generates an electromagnetic field. When a geographic zone is subjected to a relatively powerful electromagnetic field, on the one hand the effects on the other surrounding transmissions (interference) and, on the other hand, the presumed effects on the health of the persons in the neighbourhood of this zone can be feared.
Recommendations, for example the recommendations of ICNIRP (International Commission on Non-Ionizing Radiation Protection) in association with WHO, or also the decisions of ARCEP (Autorité de Régulation des Communications Electroniques et des Postes) in France, fix transmitted power limit values. These limit values depend, among other things, on the zone of use (for example for the decisions of ARCEP, Metropolitan France or other French territory), on the location of the use (inside or outside of buildings) and on the frequency band used.
There is a need, during the routing of a message in a multihop network, to limit the zones for which the power of the electric and/or magnetic fields is relatively high, or at least to know these zones.